To prevent image distortion at power on/off time in a normally white type liquid crystal display, “white” data is written into pixels at power on/off time for turning the screen white. In the case of a normally black type liquid crystal display, “black” data is written into pixels at power on/off time for turning the screen black. More specifically, at power on time, image distortion is first eliminated by turning the screen white (or black) for subsequently displaying images corresponding to display data. At power off time, image retention is first eliminated by turning the screen white (or black) for subsequently turning the screen off.
In writing “white” (or “black”) data into pixels, a conventional liquid crystal display device requires an external source from which “white” (or “black”) data is derived. The conventional liquid crystal display further requires drivers mounted on an external substrate or an external driver integrated circuit (IC) for adjusting a VCOM voltage, which is applied to a common electrode of a liquid crystal capacitor in a pixel, and a CS voltage, which is applied to an electrode adjacent to the common electrode of a storage capacitor, to “L” level.
Referring to FIG. 7, a display unit 102 having pixels arranged in a matrix is disposed on a glass substrate 101. A horizontal driver 103 is disposed below the display unit 102 for writing display data into each pixel of the display unit 102. A vertical driver (not shown) is disposed beside the display unit 102. The glass substrate 101 is electrically connected to an external substrate 105 via a flexible cable (substrate) 104.
The external substrate 105 has a timing generator (TG) 106, a VCOM driver 107, and a CS driver 108. The timing generator 106 generates various timing signals based on reference signals such as a master clock MCK, a vertical synchronization signal Vsync, and a horizontal synchronization signal Hsync that are provided by a graphic controller adjacent to a control unit. The various timing signals generated are supplied to the horizontal driver 103 and the vertical driver via the flexible cable 104. At power on/off time, the timing generator 106 generates and supplies “white” (or “black”) data to the horizontal driver 103.
The VCOM driver 107 generates a VCOM voltage in synchronization with timing signals from the timing generator 106, and applies the VCOM voltage to each common electrode of a liquid crystal capacitor in all pixels via the flexible cable 104. The CS driver 108 generates a CS voltage in synchronization with timing signals from the timing generator 106, and applies the CS voltage to the electrode adjacent to the common electrode of a storage capacitor in all pixels via the flexible cable 104. At power on/off time, both the VCOM driver 107 and the CS driver 108 adjust the VCOM voltage and the CS voltage, respectively, to a low level.
In a conventional liquid crystal display device, as described above, the external substrate 105 (or an external driver IC) is interposed between a control unit and the liquid crystal display device for preventing an image distortion at power on/off time. Moreover, a circuit for generating “white” (or “black”) data and circuits for adjusting the VCOM voltage and the CS voltage to a low level are mounted on the external substrate 105 (or an external driver IC). This prevents a reduction in size and costs associated with the system as a whole, due to the steps involved in disposing the external substrate 105, as well as mounting the timing generator 106, the VCOM driver 107, and the CS driver 108 thereon.
Accordingly, an object of the present invention is, while enabling a reduction in size and costs associated with the system as a whole, to provide a liquid crystal display device that can start displaying images without image distortion at power on time, a liquid crystal display device that can turn the screen off without image retention at power off time, a method of controlling the liquid crystal display device, and a mobile terminal incorporating the liquid crystal display device as a screen display.